This invention relates to apparatus and methods for communicating and displaying image data, and more particularly relates to apparatus and methods for communicating and displaying compressed image data.
As digital image processing technology has advanced in recent years, documents and images are increasingly being created, stored and displayed electronically. Indeed, commonly available computer programs such as word processors, page layout, graphics arts, photo editing and other similar programs may be used to create, edit, save and display electronic documents and images (collectively referred to as “electronic documents”). In addition, commonly used electronic devices such as digital scanners, digital copiers and digital cameras may be used to create and save electronic documents. As a result, the number of electronic documents that are created each year grows at an extremely rapid rate.
Further, improvements in image processing technology have resulted in significant improvements in electronic document image quality. Indeed, electronic images are frequently created at resolutions of 1200 dots per inch (“dpi”) or more. As image resolution has increased, the amount of data required to represent high quality images also has increased. For example, a single page containing an 8″×10″ image having four color separations (e.g., cyan, magenta, yellow and black) and a resolution of 1200 dpi includes more than 109 mega-pixels for each color separation, and may include more than 436 mega-bytes (“MB”) of data.
Because of the large amount of data required to represent high quality images, it is not practical to store such information in an uncompressed state. Thus, applications and devices that create and store high quality digital color images typically do so in a compressed format. In particular, as a result of the development of block compression standards such as JPEG (an acronym for “Joint Photographic Experts Group”), many digital imaging systems and applications create, convert, and/or maintain digital content in a JPEG compressed format (referred to herein as “JPEG data”). Depending on the image, it often is possible to achieve very high compression ratios. For example, the image described above that includes 436 MB of uncompressed data may be compressible to approximately 40 MB of JPEG data.
One such digital imaging system that converts and maintains digital content in compressed form is a digital printing system, an example of which is illustrated in FIG. 1. In particular, digital printing system 10 includes document source 12, print server 14, client computer 16 and printer 18. Document source 12 may be a personal computer, color scanner, electronic document archive, or other source of electronic documents 20, and print server 14 may be a conventional print server, such as those manufactured by Electronics for Imaging, Inc. (Foster City, Calif.) under the trademarks Fiery®, EDOX® and Splash®. Document source 12 provides electronic document 20 to print server 14 for printing on printer 18.
Electronic document 20 may include data in a page description language (“PDL”), such as PostScript, portable document format (“PDF”), page command language (“PCL”) or other PDL. Print server 14 includes raster image processor (“RIP”) 22 that converts electronic document 20 from PDL format to raster data in a compressed format. For example RIP 22 may convert the PDF data to block-compressed raster data (e.g., JPEG data) in compressed file 24, which may be stored in memory 26. To print the electronic document, RIP 22 may retrieve compressed file 24 from memory 26, decompress the file, and provide the decompressed raster data to printer 18 for printing.
Prior to printing, it often is desirable to display all or part of the raster image data contained in compressed file 24. For example, it may be desirable to display all or part of compressed file 24 on client computer 16 to visually proof the raster image data. Client computer 16 may be part of print server 14, or may be separate from print server 14. For example, print server 14 may be located at a printshop, and client computer 16 may be located at a customer office. Client computer 16 may communicate with print server 14 via communication channel 28, such as a local area network, wide area network, the Internet, or other similar network. Depending on the size of compressed file 24 and the bandwidth of communication channel 28, however, it may be impractically slow to transfer compressed file 24 to client computer 16 for display. For example, if compressed file 24 is a 40 MB file, and communication channel 28 is a conventional digital subscriber line (“DSL”) or cable broadband connection, it may take more than ninety seconds or more to download and display the file on client computer 16.
To solve this bandwidth problem, some previously known digital printing systems create a reduced resolution (often referred to as a “thumbnail”) image of the raster image data, and then transfer only the thumbnail image to client computer 16. Because the file size of the thumbnail image is much smaller than the size of compressed file 24, the download time is much faster than that required to transmit the entire compressed image file. Although the thumbnail image may be useful for verifying very general qualities of the image in compressed file 24, the resolution of the thumbnail image is typically insufficient for proofing purposes. Further, because the resolution of the thumbnail image is fixed, a user cannot zoom in or out to view the image at multiple resolutions.
Another previously known digital imaging system attempts to solve the limited bandwidth problem by encoding and communicating only a subset of high resolution image data. For example, Dekel et al. U.S. Pat. No. 6,314,452 (“Dekel”) describes an imaging system that includes a server that encodes a region of interest (“ROI”) of an uncompressed image, and then transmits only the compressed ROI data to a remote client computer via a communication network. This previously known technique assumes that a desired ROI is less than the entire image, and therefore the server only compresses and communicates data associated with the ROI. One problem with this technique, however, is that all of the image data are never entirely compressed. As a result, such systems are incompatible with digital imaging systems, such as digital printing system 10, that include print servers that compress and store all of the raster image data. In addition, because the Dekel system never compresses an entire image, the system requires very large storage devices.
In view of the foregoing, it would be desirable to provide methods and apparatus that allow fast communication and display of compressed raster image data.
It further would be desirable to provide methods and apparatus that allow fast communication and display of compressed raster image data at full resolution.
It additionally would be desirable to provide methods and apparatus that allow fast communication and display of compressed raster image data at multiple resolutions.
It also would be desirable to provide methods and apparatus that allow fast communication and display of raster image data that has been fully compressed.